1. Field of the Invention
The present invention relates to generally a perpendicular magnetic recording type disk drive and more particularly to a disk drive composed of a double-layered perpendicular magnetic recording type disk medium and a read head including an MR element.
2. Description of the Related Art
In recent years, public attention has been paid to a perpendicular magnetic recording as a technology for surpassing the limit of recording density of conventional longitudinal magnetic recording in the field of a disk drive represented by the hard disk drive. In this field of the perpendicular magnetic recording system, a disk drive which employs a double-layered disk medium (hereinafter referred to as disk) as its recording medium has been developed for practical application.
The double-layered disk has a recording magnetic layer possessing perpendicular magnetic anisotropy and a soft magnetic layer provided between the recording magnetic layer and a substrate. At the time of data recording operation, the soft magnetic layer has a function for supporting the head recording action by passing part of magnetic flux generated from a magnetic pole of the head to the other magnetic pole. In the double-layered disk, when the magnetic head is executing its read operation, magnetization of the soft magnetic layer, which is a bottom portion of the recording magnetic layer and the read head element are magnetically coupled with each other and operated. As a result, principally, a larger read magnetic field is generated than in case where there is no soft magnetic layer.
Today, the perpendicular magnetic recording type disk drive, which employs such a double-layered disk based on the perpendicular magnetic recording system and a magnetic head having a read head element composed of a giant magnetoresistive (GMR) element, has been developed for its practical purpose (see, for example, U.S. Pat. No. 5,933,297 and U.S. Pat. No. 6,125,019). Meanwhile, in an ordinary longitudinal magnetic recording type disk drive, a magnetic head in which the read head element and an inductive write head element are mounted on a slider thereof is used as a read/write head.
The conventional GMR element has been developed so as to be adapted to the longitudinal magnetic recording type disk whose recording magnetic layer is relatively thin. When a recording signal recorded magnetically in a perpendicular direction to a disk surface is reproduced by means of this conventional GMR element, there may occur such a problem that saturation phenomenon of the GMR element occurs so that a read signal waveform from the read head element is distorted. This phenomenon is estimated to be generated because a GMR element action point is shifted due to leaking magnetic field from a uniformly magnetized region except a transition to recording magnetization in the recording magnetic layer on the disk, so that response dynamic range of the read head element is narrowed correspondingly.
Because according to the longitudinal magnetic recording method, magnetic field applied from such uniformly magnetized region to the GMR element is substantially zero, such a problem has been never generated. That is, this problem is particular to a case where the disk having perpendicular magnetic anisotropy and the GMR element (including the MR element) acting as a read head element are combined.
As described above, in the double-layered disk, when the magnetic head executes a read operation, a larger read magnetic field occurs than in case where there is no soft magnetic layer, because of the magnetization state of that soft magnetic layer which is a bottom portion of the recording magnetic layer. As a result, an allowance to the saturation of the GMR element is small. Under this condition, leaking magnetic field (uniform magnetic field) from an adjacent track recorded in a single direction is added to a reading object track on a disk, thereby possibly causing the saturation of the GMR element.